Automotive powertrains, particularly powertrains used with front wheel drive vehicles and featuring an engine and transaxle mounted in a conventional east-west direction—i.e., with the engine's crankshaft perpendicular to the longitudinal center line of the vehicle—utilize roll restrictors to prevent unwanted rotation of the engine and transaxle about an axis which, if not coincidental with the engine's crankshaft center axis, is at least parallel thereto.
Known automotive powertrain roll restrictors utilize brackets for attaching the roll restrictor to the transaxle or engine. An example of known roll restrictor bracket is described in published US patent application US2015/152953 and shown in FIG. 1.
Downsized powertrains such as those including a three-cylinder engine are inherently imbalanced due to increased roll/yaw motion as compared to four-cylinder engines. To address the increased roll/yaw motion, it is necessary to minimize the translational and especially the rotational stiffness of the roll restrictor system.
One way of reducing translational and rotational stiffness of the roll restrictor system is to use a softer material in the rubber bushes that mediate attachment of the roll restrictor bracket to the engine or transaxle. However, use of a softer material, while providing noise, vibration and harshness (NVH) benefits may result in a decrease in durability and lifespan of the rubber bushes due to rotational wear of the bushes as they rotate in the roll restrictor bracket.
Rotational wear can be partially addressed by pressing a sleeve into the roll restrictor bracket and pressing the rubber bush into the sleeve as described in published US patent application US2015/0283891. However, such a configuration does not adequately address rotational wear of the rubber bush as it is still able to rotate relative to the sleeve. Furthermore, the sleeve would wear as it rotates relative to the roll restrictor bracket. Under cornering load the rubber bush may become displaced laterally relative to the engine or transaxle risking failure of the connection therebetween. The application of heat from the powertrain further exacerbates the issues of low durability and increased failure risk.
It is against this background that the present invention has arisen.
An aspect of the invention provides a roll restrictor system for an automotive powertrain, comprising: a torque roll restrictor bracket configured for attachment to the automotive powertrain; wherein attachment is mediated by a bushing; wherein the bushing is provided within a bearing which facilitates rotation of the bushing within the torque roll restrictor bracket.
Use of a bearing in which the bushing is mounted significantly reduces rotational strain on the bushing, thus greatly increasing the durability thereof. Furthermore, the reduced rotational strain exhibited by the bushing enables a softer material to be used thus providing noise, vibration and harshness (NVH) benefits.
The bushing may be a voided bushing. Use of a voided bushing may result in greater softening of the rubber material at temperature as compared to a solid bushing. Softening of the rubber results in reduced translational and rotational stiffness of the roll restrictor system and improved NVH benefits.
The voided bushing may comprise at least two arms which support the voided bushing in an opening through the torque roll restrictor bracket. The at least two arms may comprise four arms. The use of arms to interface with the bearing provides at least two points of contact between the bushing and the bearing thus further reducing the rotational and translational stiffness of the bushing.
The bushing may be a solid bushing. Use of a solid bushing imparts lesser strain to the bushing as compared to a voided bushing due to having more material than a comparable voided bushing and consequently a greater stiffness.
The bearing may be a ball-bearing. Use of a ball bearing is advantageous as the bearing is inserted into the inner ring of the ball bearing. The inner ring rotates relative to the race and the bushing is not in direct contact with any moving surface. Therefore, the longevity of the bushing is increased due to the only cause of wear being a small degree of repetitive rotation of the bushing within the inner ring as the powertrain moves relative to the roll restrictor bracket. The ball bearing may be a self-aligning ball bearing. Use of a self-aligning ball bearing allows for both low rotational and transitional stiffness in the bushing thus further increasing durability of the bushing.
The bearing may be a roller bearing. Use of a roller bearing is advantageous as the bearing acts directly on the bushing, or a sleeve within which the bushing is pressed. A tight fit between the rollers and bushing dictates that the rollers cannot detach from the bearing under normal loads. Roller bearings are durable and accurate and the friction produced in use is minimal as compared to other types of bearing.
The roll restrictor bracket may be attached to the powertrain in at least two places and to a vehicle chassis or sub-frame in at least one place. The bearing may have an outer surface that is coated with a vibration absorbing material.
Coating of the outer surface of the bearing with a vibration absorbing material provides additional NVH benefits which may be desirable in certain applications where noise, vibration or harshness is recognised as a problem.